High-speed generators are used in many applications, including on gas turbine engines for aircraft, ships, and military vehicles. Such generators typically rotate at relatively high speeds (e.g., 12,000 r.p.m. to 24,000 r.p.m. or greater) during operation. While high-speed generators are generally safe and reliable, they may have drawbacks in certain circumstances. Large centrifugal forces may be imposed upon the generator's rotating parts, such as the rotor. One such generator rotor has four poles, each of which is wound with wire conductors, called windings. During operation of the generator, the windings that rotate with the rotor are subjected to these relatively high centrifugal forces, which may cause the windings to separate from the rotor. The centrifugal forces may also cause the rotor to become improperly balanced and thus off-center as it spins during generator operation. Improper balancing of a rotor in particular can result in inefficiency in the operation of the generator, and may in extreme circumstances cause generator failure.
To secure the windings against such centrifugal forces, it is known to mount support wedges between each of the respective poles. Although these support wedges assist in containing the windings against the pole body so as to oppose the centrifugal force during rotation of the rotor, they too experience high centrifugal forces. The centrifugal forces may cause the support wedges to slip radially outward away from the shaft of the rotor, thus limiting the ability of the support wedges to secure the windings against the pole body. Particularly if the axial length of a conventional rotor is relatively large in comparison with its diameter, the centrifugal forces may cause significant radial deflection or flexure of the support wedges near the rotor's axial midpoint.
In order to prevent the support wedges from slipping radially outward, a conventional rotor may use bands around the outer diameter of the rotor to retain the support wedges. In another conventional rotor, an “underwedge” system may be employed in which the support wedges extend in their arc length all of the way between neighboring pole tips on the rotor and snap rings are then used to hold the support wedges in place relative to the poles.
These conventional structures for retaining support wedges in place on the rotor are limited in their effectiveness in high-speed generator applications. Both the bands used to retain the support wedges and the components of the underwedge systems (particularly the snap rings) also can suffer from bending from centrifugal forces and therefore may provide only a limited amount of counteracting force to keep the support wedges in place and may create an additional imbalance in the rotor. Additionally, because it is difficult to accurately control the positioning of, and the amount of pressure applied by the bands and underwedge componentry, it may be difficult to accurately set and maintain the positioning of the support wedges and to control the concentricity of the various support wedges around the rotors during operation of the generator. If the support wedges are not concentric (or evenly-spaced) about the rotor's axis, then the spinning rotor assembly will be out of balance.
Also during operation of the generator, current passes through the wire windings, thereby generating heat. Some of this heat should be removed from the generator, particularly from the windings, to allow efficient operation of the generator and to keep the wire winding temperature below the point where the wire's insulation begins to break down. If an insufficient amount of heat is removed from the generator, then the power output from the generator may be limited and the insulation of the wires within the generator may degrade. Conventional cooling systems such as air or limited conduction, or spray of the rotor core may, under certain circumstances, not offer sufficient heat dissipating capacity for the high speed generators.
Accordingly, there is a need for a novel rotor assembly and method that will permit a high-speed generator to work at optimum efficiency. There is also a need for a novel rotor assembly and method that will provide improved securing of support wedges on a rotor even at high speeds of operation so that the support wedges will continue to provide support for and direct pressure toward the generator windings. There also is an additional need for a novel rotor assembly and method that will accurately set and maintain the positioning of the support wedges and control the concentricity of the various support wedges mounted around the rotor during operation of the generator. There is an additional need for a novel rotor assembly and method that do not have components that have a tendency to increase rotor imbalance. There is a further need for a novel rotor assembly and method that substantially cool the generator during operation thereof. The present invention fulfills one or more of these needs and may provide other related advantages.